1. Field of the Invention
This invention relates to a technique for determining a discharge state where liquid is discharged from a nozzle and a non-discharge state where the liquid is not discharged.
2. Description of the Related Art
In a technique in which processing is performed by supplying liquid to a processing object (work) such as a substrate for example, it is necessary in some cases to monitor whether or not a predetermined amount of the liquid is supplied at a predetermined timing. A technique for determining whether or not liquid is discharged from a nozzle is, for example, described in each literature below.
In a technique described in JP2002-316080A, a discharge port of a nozzle is imaged by a camera. A background plate is provided at a position corresponding to the background of the nozzle when viewed from the camera and a moment of starting the discharge is detected by a change in shading appearing in an image. Further, a technique described in JP2009-095826A is a technique for inspecting a nozzle, and a thickness of a liquid column discharged in a column-like manner from the nozzle is optically detected. Specifically, reflected light of light irradiated toward the liquid column is imaged, a discharge amount (thickness of the liquid column) is determined from a luminance average value of the imaged image and the presence or absence of a variation of the discharge amount is determined from a luminance variation amount. Further, in a technique described in JP2012-009812A, a liquid column which becomes luminous by the reflection of illumination light by the liquid column is imaged. The presence or absence of the discharge, a discharge amount and the like are determined by comparing that image and reference information prepared in advance.
In each of the above conventional techniques, the discharge is determined utilizing a change of the content of an imaged image depending on the presence or absence of the discharge. However, since the processing is required to be even faster, it has become difficult to utilize such determination techniques. For example, in a configuration in which the discharge of liquid is started after a movable nozzle is positioned at a predetermined position, the start of the discharge of the liquid can be detected from a change of an image from a reference image after the positioning of the nozzle and before the discharge of the liquid. In contrast, it has also recently become necessary to discharge liquid during a movement of a nozzle or substantially simultaneously with the completion of positioning. Thus, in such a configuration, it is difficult to prepare a reference image to be compared. Further, a liquid discharge time has also become shorter for faster processing and the saving of processing liquid.
Thus, a technique has been required which can reliably determine a state of liquid from an image imaged at a certain time without depending on a comparison with an image before or after the former image or a reference image.